I tried a front sprocket from a "R" dirt bike, 1 tooth smaller I think, and it geared down too much. Maybe going up on the rear would have been better. I just learned to like the 450 in the woods. The 450 is lighter and more nimble, a trade you have to accept for the lack of low end power. If you get one with kick start, it will be a PITA when you stall-out off camber.
Don't ever hook up with your utility bike brothers for a trail ride, you will be pulling out your hair 2 turns down the trail. Their 3rd gear cruising is somewhere in between 1st and 2nd for the 450R.